bpp ⇝

bits per pixel

(bpp) The number of bits of information
stored per pixel of an image or displayed by a graphics
adapter. The more bits there are, the more colours can be
represented, but the more memory is required to store or
display the image.

A colour can be described by the intensities of red, green and
blue (RGB) components. Allowing 8 bits (1 byte) per
component (24 bits per pixel) gives 256 levels for each
component and over 16 million different colours - more than
the human eye can distinguish. Microsoft Windows [and
others?] calls this truecolour. An image of 1024x768 with
24 bpp requires over 2 MB of memory.